Electrophonic stringed musical instrument



June l2, 1934. A, J 5T|M5ON 1,962,919

ELECTROPHONIC STRINGED MUSICAL INSTRUMENT Filed April 7, 1933 2 Sheets-Sheet k1 T Lgi Eigf ATTO TEY.

kJune l2, 1934. A 1 s'nMsON 1,962,919

ELECTROPHONIC STRINGED MUSICAL INSTRUMENT Filed April 7, 1933 2 Sheets-Sheet 2 Ti Q41:

ATTORNEY.

Patented June 12, 1934 UNITED STATES PATENT OFFICE ELECTROPHONIC STRINGED MUS INSTRUMENT Arthur J. Stimson, Los Angeles, Calif., assignor to Dobro Corporation, Ltd., Los Angeles, Calif., a corporation of Calfornia Application April 7, 1933, Serial No. 664,899

13 Claims.

proved novel means for directing the vibrations of the strings to an electrical amplifier.

Another object of the invention is to provide a novel electrical pick-up bridge `and mounting therefor for stringed musical instruments.

Other objects and the advantages of this invention will be apparent from the following description taken in connection with the accompanying drawings wherein:

Fig. 1 is a top plan view of a guitar embodying the features of my invention;

Fig. 2 is an enlarged fragmentary longitudinal central section through the guitar;

Fig. 3 is a section of the bridge and its associated mounting taken on line 3-3 of Fig. 2;

Fig. 44 is an enlarged fragmentary top plan view of the guitar with the tail piece and cover removed;

Fig. 5 is a wiring diagram showing the method of electrically connecting the guitar and an electrical amplifier;

Fig. 6 is a vertical section through a modified for'm of bridge support; and

Fig. 7 is a fragmentary top plan view of the device shown in Fig. 6.

Referring to the drawings by reference characters I have indicated a guitar generally at 10. The guitar 10 includes a body 12 of the usual shape having mounted thereon the usual neck 13 and tail piece 14 on which the usual strings 15 are mounted. The body 12 includes a top 16, a bottom 17 and sides 18. The top 16 has a circular aperture 19 therein and secured to the under face of the top 16 adjacent the aperture 19 I provide a ring member 20 the inner circumference of which is of less diameter thanv that of the aperture 19 to form a shelf 21. f

Supported on the shelf 21 I provide a bridge mounting which I have indicated generally at 22. As shown the bridge mounting 22 is made in two metal sections 23 and 24 each preferably made of aluminum. The section 23 includes a vertical face plate 25 having a pair of integral horizontal legs 26 thereon. Intermediate the width of the face plate 25 and adjacent the top thereof a threaded aperture 26' is provided. The section 24 includes a vertical face plate 27 having an integral horizontal leg 28 thereon. Intermediate its width and height the face plate 27 includes a shelf member 29 which extends towards the face plate 25 and adjacent each end the face plate 27 includes a boss 30 which extends the face plate Between the ICAL towards 25.

face plates 25 and 27 I provide a U -shaped member 31 made of iron and which is magnetized to form a permanent magnet. The pole ends of the member 31 are positioned adjacent the bosses" 30 with the remainder of the member positioned below the shelf 29 which is shorter than the face plate as shown in Fig. 3.

The sections 31 are vsecured to form a rigid 23 and 24 and the magnet member together by bolts 32 and nuts 33 unit.

Positioned on the shelf 29 I provide a bridge 4member 34 which comprises a base portion 35 rial.

The bridge base 35 is of less cross-sectional width than the distance between the face plate 25 and the face plate 27 so that the base does not engage either of the face plates. Mounted in apertures one each side of the bridge base 35 I provide a plurality of spaced blocks 39 which like the member 38 vibration conducting material.

are formed of gut or other non- Intermediate the width of the base 35 and adjacent the top .thereof on one side I provide a block 40 which is a reed. The blocks 39 and 40 extend beyond the adjacent faces of the bridge base 35 and engage the adjacent face plates 25 and 27.` When the face plates 25 and 27 are secured together by the bolts 32l the blocks 39 and 40 are compressed so that the bridge is rmly retained in position.

Each of the bosses 30 on the face plate 27 includes a threaded aperture 41 in which a similarly threaded in an aperture vide a block 43 bolt 42 is positioned. Mounted in the end of each bolt 42 I prowhich like the blocks 39 is formed of gut or other non-vibration conducting material. When as sembling the bolts 42 are rotated towards the bridge until the base 35 is firmly clamped between the mocks 43. A lock nut 44 is provided on each of the bolts 42 to retain them in adjusted positions. y

Mounted in each end of the bridge base 35 adjacent the bottom thereof I provide a bar 45 which is made of paramagnetic material which may be a ferrous compound to form a magnetic core. provide a spool wire.

Mounted on each of the core bars 45 I 46 of wound electrical conducting Adjacent each of its pole en ds the vmagnet member 31 includes a threaded aperture 47 in which similarly threaded bolts 48 are positioned. The bolts 48 are made of ferrous material and are substantially coaxial with the core bars 45 of the bridge base. Positioned on each of the bolts 48 I provide a lock nut 49 for retaining the bolts-48 in adjusted positions.

Positioned in the threaded aperture 26 of the face plate 25 I provide a bolt 50 which includes a reduced portion 5l having an aperture 52 therein. Mounted in the end of the bolt 50 opposite the reduced portion 51 I provide a block 53 which like the blocks 39 is made of gut or other non-vibration conducting material.

When assembling the bridge mounting 22 and the bridge 34 in the guitar body the ends of the legs 26 and 28 rest on the shelf 21 and the strings 15 are positioned in the notches 37 of the bridge member 36. One end of an operating rod 52 is then slackly connected to the bolt 50 as at 54 and the opposite end of the rod extends out of the end of the guitar body through a suitable bearing member 55 and is provided with an enlarged operating head 56.

Mounted in the guitar body 12 I provide a valiable-resistance unit 57 which includes an operating shaft 58 and mounted on and extending through the bottom 17 I provide a pair of plugin sockets 59. As shown in Fig. 5 one end of each of the coils 46 is connected together by a wire 60 and the opposite ends of the coils are connected by wires 6l to opposite terminals 62 of the resistance unit 57. The terminals 62 of the resistance unit are each connected by a wire 63 to the plug-in sockets 59.

An amplifying unit 65'having a pair of leads 66 which terminate in plugs 67 adapted to engage the plug-in sockets59 is then operatively connected to the guitar. The amplifying unit 65 is operatively connected to an electrically actuated resonator 68 by leads 69.

The operator then actuates the strings 15 and actuates the bolts 48 closer or farther from the pole members 45 to vary the inductance between the magnet 31 and the pole members, until the desired volume is obtained. Thereafter a cover member is preferably positioned over the aperture 19.

The operating rod58 of the resistance unit 57 extends through a cover 70 and is provided with an enlarged actuating head 71. After the device is thus completely assembled the volume may be varied by operating the resistance unit 57 to vary the resistance between the wires 61 and the tone may be varied by tightening. or loosening the pressure of the plug 54 on the bridge member-34.

In Figs. 6 and 7 -I have indicated a slightly modified form of bridge supporting device generally at 75. The bridge member and its associated parts and the permanent magnet are similar to those shown and described in connection with the bridge supporting device 22 and are indicated by similarlyprimed reference characters.

As shown the bridge supporting device 75 comprises a vertical body portion 76 having a circuvlar horizontal ange 77 extending therefrom.

provide raised bosses 8l in which the bolts 42 are positioned. The flange 77 has an elongated aperture 82 therein to provide clearance for the operating rod of the bolt 50 and further includes a pair of apertures 83 to provide clearance for the bolts 42 and 48'. When assembling the bridge supporting device 75 in a guitar the outer edge of the flange 77 is supported on the shelf 21 of the guitar like the ends of the legs 26 and 28 of the bridge supporting device 22.

Although'I have shown and described my invention in combination with a guitar it will be understood that the invention may be used for recording sound on iilm or on all wax records or it may be used in combination with other types of musical instruments other than that shown and described in the accompanying description without departing from the spirit of my `invention. From the foregoing description it will be apparent that I have provided novel means for directing the vibrations of the strings of a stringed musical instrument through an electrically actuated resonator which is simple in construction and highly efficient in use.

Having thus described my invention, I claim:

1. In combination with a stringed musical instrument including abody, a permanent magnet supported. on said body, a bridge supported on said body, a pair of coil members mounted on said bridge to vibrate therewith, said coil members being spaced from the ends of said magnet and means to connect said coil members to a loud speaker.

2. In combination with a stringed musical instrument including a body, a bridge supporting device mounted on said body, a bridge member, means to support said bridge member under tension on said supporting device, means to vary the tension of said bridge, electromagnetic means including a coil and associated with said bridge and means to connect said coil to a loud speaker.

3. In combination with a stringed musical instrument including a body, a bridge, means to support said bridge on said body, a coil of electrical conductive wire mounted on each end of said bridge, a permanentv magnet member having a pair of spaced pole ends, said pole ends of said magnet being positioned one adjacent each of said coils and spaced therefrom, and means to connect said coils to a loud speaker.

4. In combination with a stringed musical instrument including a body, a bridge mounted on and sound insulated from said body, paramagnetic core members mounted on said bridge at opposite ends thereof, a coil of'electrical conducting wire surrounding each of said core members, one end of each of said coils being connected together, the opposite ends of each of said coils being adapted to be connected to an electrically actuated resonator, and a permanent magnet having a pair of spaced pole ends mounted on said supporting device, said pole ends of said magnet -being positioned one adjacent each of said core members and being spaced therefrom.

I 5. In combination with alstringed musical instrument, va bridge member adapted to be engaged by the strings'of said musical instrument, means to support said bridge, paramagnetic core members mounted on said bridge at opposite ends thereof, a coil of electrical conductive wire surrounding each of said cores, one end of each of said coils being connected, a permanent magnet member having a pair of spaced pole ends, positioned one adJacent each of said cores and spaced therefrom, means to vary the magnetic gap between said pole ends of said magnet and said core members, means to connect the opposite ends of said coils to an electrically actuated resonator.

6. In combination'with a stringed musical instrument including a body, a bridge supporting device mounted on said body, a dlamagnetic bridge member engaged by the strings of said musical instrument, said bridge being supported by said supporting member, means to clamp said bridge in position on said supporting device, means to vary the tension of said clamping means on said bridge at opposite ends thereof, a coil of electrical conductive wire at each end of said bridge, one end of each of said coils being adapted to be operatively connected to an electrically actuated resonator, and a permanent magnet member having a pair of spaced pole ends mounted on said supporting device, said pole ends of said magnet being positioned one adjacent each of said core members and being'spaced therefrom.

7. In combination with a stringed musical instrument, a/bridge member adapted to be engaged by the strings of said musical instrument, means to support said bridge, paramagnetic core members mounted on said bridge at opposite ends thereof, a coil of electrical conductive wire surrounding each of said cores, one end of each of said coils being connected, a permanent magnet member having a pair of spaced pole ends, means to support said magnet, said pole ends of said magnet being positioned one adjacent each of said cores and being spaced therefrom, means to vary the magnetic gap between said pole ends of said magnet and said core members, means to connect the opposite ends of said coils to an electrically actuated resonator there being a variable resistance unit operatively connected across said opposite ends of said coils.

8. In combination with a stringed musical instrument including a body, a bridge supporting device mounted on said body, a diamagnetic bridge member engaged by the strings of said musical instrument and mounted on said supporting device, means to rigidly clamp said bridge member to said supporting device, paramagnetic core members mounted on said bridge at opposite ends thereof, a coil of electrical conducting Wire surrounding each of said cores, one end of each of said coils being connected, a permanent magnet member having a pair of spaced pole ends, said pole ends of .said magnet being positioned one adjacent each of said core members and spaced therefrom, means to vary the magnetic gap between said pole ends and the i adjacent core members and leads extending from of electrical conductivewire surrounding eachof said core members, one end of each of said coils being connected together, means to connect the opposite ends of each of said coils to an electrically actuated resonator, a variable resistance unit operatively connected across said opposite ends of said coils, a permanent magnet member having a pair of spaced pole' ends mounted on said supporting device, said pole ends of said magnet being positioned one adjacent each of said core members and being spaced therefrom and means to vary the magnetic gap between said pole `porting device, paramagnetic core members mounted on said bridge at opposite ends thereof, a coil of electrical `conductive |wire surrounding each of said core members, one end of each of said coils being connected together, means to connect the opposite ends of each of said coils to an electrically actuated resonator, a permanent magnet member having a pair of spaced pole ends mounted on said supporting device, said pole ends of said magnet being positioned one adjacent each of said core members and being spaced therefrom and means to vary the magnetic gap between said pole ends and said core memers.

11. In combination with a stringed musical instrument including-a body, a bridge supporting device, means to mount said supporting device on said body, said supporting device comprising two sections secured together, a diamagnetic bridge member adapted to be engaged by the strings of said musical instrument, said bridge being supported by one of said supporting device sections and being clamped between said two supporting device sections, a plurality of sound insulating members interposed between said bridge and said supporting device sections, bolts adjac'ent opposite ends of said bridge supported by one of said supporting device sections, said bolts being adapted to exert pressure on opposite ends of said bridge, sound insulating means interposed between said bolts and said bridge, a permanent magnet member mounted between said supporting device sections and secured thereto, paramagnetic core members mounted on said bridge at opposite ends thereof, a coil of electrical conducting wire surrounding each of said core members, one end of each of said coils being connected, said magnet member having a pair of spaced pole ends and said cores, a pair of electrical connector sockets on said body, the opposite ends of said coils being electrically connected one each to said cnnector sockets, a variable resistance unit operatively connected across said opposite coil ends, said connector sockets being. operatively connected to an electrically actuated resonator through an amplifying device.

12. In combination with a stringedmusical instrument including a body, a bridge supporting device, means to mount said'supporting device on said body, said supporting device comprising two sections secured together, a diamagnetic` bridge member adapted to be engaged by the strings of said musical instrument, said bridge being supported at its base by one of said supporting device sections and being clamped between said two supporting device sections, a plurality of vibration insulating members interposed between said bridge and said supporting devicesections, bolts adjacent' opposite ends of said bridge supported by one of said supporting device sections, said bolts being adapted to exert pressure on opposite ends of said bridge, vibration insulating means interposed between said bolts and said bridge, a tension bolt, said tension bolt being mounted on one of vsaid supporting device sections and positioned intermediate the length of said bridge, said tension bolt being adapted to apply pressure to one face of said bridge and vibration insulating means interposed between said tension bolt and said bridge, a permanent magnet mounted between said supporting device sections and secured thereto, pararnagnetic core members mounted on said bridge at opposite ends thereof, a coil of electrical conducting Wire surrounding each of said core members, one end of each of said coils being connected, said magnet member having a pair of spaced pole ends positioned one adjacent eachof said core members and spaced therefrom, means to vary the magnetic gap between said pole ends and said cores, a pair of electrical connector sockets on said body, the opposite ends oi.' said coils being electrically connected one each to said connector sockets, a variable resistance unit operatively connected across said opposite coil ends, and means to connect said connector sockets to an amplifying device.

13. In combination with a stringed musical instrument including a body, a pick up device comprising a magnet supported on said body, a bridge member supported on said body, and a coil member mounted on said bridge to vibrate therewith, said coil member being disposed in the field of saidmagnet and adapted to vibrate transverse to said field.

ARTHUR J. STIMSON. 

